Frequently the production of items that require a plurality of working steps for their manufacture is carried out on a specially designed production line, where the various working steps are performed at consecutive working stations in a prescribed order. The working steps might be machining the object, inspecting the object, assembling additional components to the object etc. The arrangement of the production line of this kind is particularly useful when the manufacturing process is work intensive and includes a variety of working steps of various kinds. A typical example where such a production line is useful and frequently applied is for assembling, in particular assembling electronic items. Long ago production lines was operated by humans, with one person at each working station performing an isolated working step and then passing the object to the neighbouring person for the next working step, usually via an intermediate storage reachable by both persons. Such manually operated production lines are still common in countries where labour costs are low.
Due to increased labour costs, in particular in industrialized countries it has for many decades been a development to replace manually operated production lines with lines operated by industrial robots.
Traditional robot automation in a production line, however face various problems. It is inflexible and takes a long time to engineer. Time consuming activities include designing safety equipment, such as fences and emergency step chains, fixtures for accurate positioning and feeding solutions to get parts in and out of the robot cells, such as conveyors and feeders.
There exist various examples of production lines having working stations operated by humans as well as working stations operated by robots.
DE 43 20 704 discloses a production line with three consecutive cells, of which two are manually operated and one automatized cell. The objects are moved from one working station to the next by rotating working tables.
In the device of EP 737 543 all working stations along the production line are automatized. The stations 51-59 are called mounting machines. Then there is a plurality of intermediate satellite chargers 61-68. Each of these chargers is manually charged (see FIG. 2). However, the part of each satellite charger that constitutes a working station in the production line does not involve manual operation. Therefore the production line as such can be considered to contain only automatized working stations. Furthermore it is not mentioned that the working stations are arranged for robot operation. Finally the movement of the objects is not carried out by the stationary operators but is performed by a transport band.
Also in US 2002/15 7241 the objects are transported by means of a conveyer and not by the stationary operators. The working stations are not arranged such that the stationary operators can move the objects from one working station to the next. In particular the manually operated working station is located far away from the robot operated working stations.
In EP 174 545 the objects are not transported by the stationary operators, but by an endless conveyer as in L1 of FIG. 10 or by an alternative charger as in L2 of FIG. 10). Further it is not mentioned that robots are engaged and there is no mixing between manual and automatized working stations. In L1 all working stations are automatized, whereas in L2 all working stations are manual.
Where human and robots are mixed in a production line they are arranged separated a large distance from each other according to prior art. See for example US 2002/157241 mentioned above. This is due to safety reasons. If a robot and a human work so close to each other that they are within reach of each other there is a risk that the human might be injured by the robot. However the localization of the robots and the humans separated far from each other entails drawbacks, such as that a large area is occupied by the production line and that some kind of conveyer means is required.
The object of the present invention is to provide a production line where humans and robots are mixed, has a high degree of safety and solves the problems related to known mixed production lines.